This invention relates to the recovery of data received by a radio frequency (RF) communication. More specifically, the invention is directed to the acquisition of synchronization for received RF frames of data and is especially, but not exclusively, suited for synchronization of data transmitted in frames of variable data rate, e.g. frames with data encoded by variable coding and modulation (VCM).
Various types of RF communication systems exist. In a known RF system, the data to be conveyed is carried by the transmission of a plurality of consecutive frames where each frame contains a header and a payload, where each payload contains a segment of the data. A preamble is typically transmitted as part of the header as an aid to determining synchronization by a receiver. In view of overhead efficiency and maximizing data throughput, the number of bytes in the preamble should be small. In RF environments where the signal-to-noise ratio (SNR) is low or is at least periodically low at the receiver, VCM is useful since the modulation rate can be changed from frame to frame based on the SNR and the resulting reliability of data recovery. When the RF communication channel has a high SNR, a modulation technique can be utilized to convey a high data throughput; conversely, when the RF communication channel has a low SNR, the modulation technique can be adjusted to convey a lower data throughput, thus maximizing the amount of reliable data throughput dependent on the RF communication channel SNR.
While VCM and other variable length frame/modulation techniques are useful in maximizing data throughput, it creates a challenge at the receiver in recovering the correct carrier frequency/timing for decoding the data carried by each frame, especially for RF environments with low SNR, since each frame may use a different modulation technique and/or independent lengths. For example, the number and/or type of symbols carrying data in the payload of one frame may differ from the number/type of symbols carrying data in the payload of a following frame. Therefore, there exists a need for improvements in acquiring and maintaining synchronization for data recovery, and especially in such systems.